In the given triangle ABC ,
Sum of the angles of of a triangle is 180 degrees.
Therefore,
[tex]\begin{gathered} \angle A\text{ + }\angle B\text{ + }\angle C\text{ = 180} \\ \angle A\text{ + 105 + 15 = 180} \\ \angle A=\text{ 180 - 120} \\ \angle A\text{ = 60} \end{gathered}[/tex]
By using sine rule,
[tex]\frac{a}{\sin A}\text{ = }\frac{b}{\sin B}[/tex]
Substituting the given values in the given equation,
[tex]\begin{gathered} \frac{a}{\sin60}\text{ = }\frac{2}{\sin 105} \\ a\text{ = }\frac{2\sin 60}{\sin 105} \\ a\text{ = 1.7931 } \\ a\text{ }\approx\text{ 1.8 }cm \end{gathered}[/tex]
